Detectors are used to detect radiation and provide spatial mapping of radiation intensity in radiation-based imaging systems. Such systems involve detection of incoming radiation, such as X-rays, gamma photons or particles, in a wide range of different applications, including medical applications.
Basically, a radiation source generates a beam in the direction of an object to be examined and a detector measures the intensity of the beam after it has passed through the object. The detector outputs information required to produce an image representing attenuation of the radiation resulting from absorption and scattering by the object through which the beam traveled. Apart from forming a transmission image of an object a detector could also be used for measuring radiation doses.
Many radiation systems involve radiation sources, such as X-ray tubes or radiation treatment machines, associated with a very high MeV photon flow during the output pulse. The challenge is to convert as many as possible of the incident high energy photons, while at the same time preserving their spatial information, with a high precision. This makes it very difficult to achieve sufficient image quality.
A detector for detecting photons in the energy range 1 keV to 100 MeV is disclosed in [1]. The detector includes at least two converter layers adapted to interact with incident X-ray photons and to cause electrons to be emitted therefrom. At least one amplifier is adapted to interact with the emitted electrons and produce a multiplicity of secondary electrons and photons representing a signal proportional to the incident fluence of X-ray photons.
Document [2] is directed towards reducing spread of electrons as compared to conventional radiation detectors. The radiation detector comprises a gas electron multiplier (GEM) using interaction between radiation and gas through photoelectric effects. The GEM is arranged in a chamber filled with gas and has a single gas electron multiplication foil arranged in the chamber. This gas electron multiplication foil is made of a plate-like multilayer body composed by having a plate-like insulation layer made of a macromolecular polymer material having a thickness of 50-300 μm and flat metal layers overlaid on both surfaces of the insulation layer. The plate-like multilayer body is provided with a through-hole structure.
Document [3] discloses converter unit configured to convert incident photons into electrons. The converter unit comprises multiple blind holes forming respective ionization chambers. In additional embodiments, the converter unit is arranged in a detector, such as an X-ray detector or absolute radiation dose measurement detector, additionally comprising an electron amplification device and/or a readout device.
Document [4] discloses a detecting unit for detecting ionizing radiation. The detecting unit comprises a converter unit for the amplification of ionizing radiation and a read-out unit. The converter unit comprises a converter and a gas-electron multiplier. The converter comprises a substrate with an ionizing radiation-receiving major surface and an electron-emitting major surface and a stack of accelerator plates in contact with the electron-emitting major side. The stack comprises a plurality of perforated accelerator plates wherein the perforations of the perforated accelerator plates are aligned to form a matrix of blind holes.